Diastolic dysfunction followed by systolic dysfunction leading to dilated cardiomyopathy (DCM) has been documented with surprisingly high frequency in HIV infected individuals. The pathophysiologic mechanisms responsible for HIV DCM are not well understood. We received 3 years of initial RO-1 funding to clarify the potential direct contribution of HIV to myocardial dysfunction by studying the effects of the recombinant HIV envelope glycoprotein, gp120, on adult rat ventricular myocytes (ARVM). Reviewers of our previous renewal application raised concerns about the clinical relevance of the short-term effects of gp120 on ARVM in vitro. Accordingly, the Co-PI (Hong Kan, MD, PhD) traveled to Lausanne, Switzerland to receive advanced training in sophisticated in vivo techniques in awake rats through a collaboration with the Swiss Cardiovascular Research and Training Network (SUK). We now report: (1) diastolic dysfunction in vivo 48 hrs following intravenous injection of HIV gp120 associated with (2) p38 MAP kinase activation and (3) iNOS protein and followed by (4) systolic and (5) diastolic dysfunction in vivo for at least 12 days following iv injection of gp120. These data complement the novel results of our initial 3 yrs of RO-1 funding to study the negative inotropic effect of gp120 on ARVM mediated through a novel CXCR4-p38MAPkinase-iPLA2-froponin I signaling pathway that supports our initial hypothesis: HIV gp120 regulates cardiac myocyte function through a novel signaling pathway. However, our new Specific Aims focus on more clinically relevant in vivo and ex vivo approaches: (I) Establish the time course of the effects of intravenous injection of HIV gp120 on cardiac systolic and diastolic function in vivo using catheter-based hemodynamic monitoring and echocardiography. (II) Determine the effects of intravenous injection of HIV gp120 on isolated adult rat ventricular myocyte (ARVM) and papillary muscle systolic arid diastolic function. (Ill) Elucidate the signaling pathways involved in the systolic and diastolic effects of intravenous injection of HIV gp120 on adult rat ventricular myocytes (ARVM). The successful completion of these Specific Aims will provide the insights necessary to perform focused interventional studies in this newly identified HIV cardiomyopathy model and potentially lead to clinical trials in humans with HIV cardiomyopathy.